The invention relates to a cathode ray tube comprising an evacuated glass envelope containing an electron gun to generate an electron beam for scanning a target. The electron gun includes a first electrode and of a cathode unit comprising a cathode support to which a cathode shaft having a cathode filament is connected. The cathode support is secured to the first electrode.
Such cathode ray tubes may be, for example, television camera tubes, television picture display tubes, or oscilloscope tubes. In a television camera tube the target usually is a photosensitive layer on a signal electrode. In a display tube the target is a display screen comprising one or more phosphors which are provided, for example, in a pattern of lines on the inside of the display window of the envelope.
Such a cathode ray tube, in the form of a television camera tube, is disclosed in Netherlands Patent Application No. 7807757 corresponding to U.S. Pat. No. 4,309,638. The cathode in the television camera tube described in this Patent Application is connected in a cathode supporting bush by means of a disc of insulation material. This cathode supporting bush is connected with its end face against a part of a first electrode, a sleeve-like anode, extending perpendicularly to the axis of the tube, which part of the anode in turn is placed against a surface part of the inner wall of the envelope extending perpendicularly to the axis of the envelope. Before they are connected, the anode and the cathode supporting bush are movable radially with respect to each other and are hence adjustable. The disadvantage of such a construction is that when such a sleeve-like anode is used the diameter of the envelope must increase stepwise in two directions. This presents probelms in manufacturing the envelope. Moreover, the construction of the cathode support is complicated and not suitable for mass production.